Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$168.28	12.539%	$189.3806	$189.38	$189.40	$189.40
Purchase #2	$45.45	10.648%	$50.2895	$50.29	$50.30	$50.30
Purchase #3	$18.90	7.813%	$20.3767	$20.38	$20.40	$20.40
Purchase #4	$110.47	7.658%	$118.9298	$118.93	$118.95	$118.90
Purchase #5	$70.55	3.180%	$72.7935	$72.79	$72.80	$72.80
Purchase #6	$179.85	5.626%	$189.9684	$189.97	$189.95	$190.00
Purchase #7	$19.39	5.505%	$20.4574	$20.46	$20.45	$20.50
7 purchase totals =	$612.89		$662.1959	$662.20	$662.25	$662.30